Test-retest & Inter-rater Reliability of Persian Version of Pediatric Balance Scale in Children with Spastic Cerebral Palsy.

Objectives Children affected with spastic cerebral palsy suffering a lot of movement and balance difficulties. Balance is one of the essential variables of movement, which facilitates functional skills. The main purpose of this study was inter-rater & test-retest reliability of Pediatric Balance Scale (PBS) in children with spastic cerebral palsy. Materials & Methods In this analytical-descriptive research performed in the rehabilitation centers, south of Tehran, Iran in 2016, psychometric method was used. For investigating the inter-rater reliability, two examiners performed the scale simultaneously with 50 children with spastic cerebral palsy. Moreover, to investigate the test-retest reliability, the scale was implemented by one examiner, in two different sessions, among 50 children with spastic cerebral palsy. There was a two-week period between the first and the second session. Results The inter-rater reliability (ICC=0.99), as well as the test-retest reliability (ICC=0.99), was quite high. Standard Error of Measurement (SEM) was acceptable for either test-retest or inter-rater reliability. Conclusion PBS is appropriate for measuring functional balance in children with spastic cerebral palsy with mild to moderate motor impairment.


Introduction
Cerebral palsy is non-progressive brain damage arises before, in the process of, or after birth (1).
Cerebral palsy is one of the factors causing disability in childhood, which impacts bodily posture as well as movement and leads to child's restriction of activity and participation (2). This restriction is the product of non-progressive disorder that occurs in the brain. Out of every 1000 successful births, two births result in cerebral palsy (3). Statistics reveal that 70%-80% of cerebral palsy cases are spastic (4).
Children with spastic cerebral palsy, have diverse difficulties specifically in movement and balance (5). In cerebral palsy, impaired movement is often accompanied by weak balance (6). Balance is the safeguarding of a posture in one specific direction, which is one of the necessary variables of movement. Moreover, balance increases the ability in functional skills (7). Balancing reactions, whether static or dynamic, are weaker in children with cerebral palsy than healthy ones (8). Children with spastic cerebral palsy have abnormal muscle tone as well as postural control. Both of these conditions affect functional balance (9). Functional balance is one of the variables of postural stability that allows the child to safely and independently perform all his/her daily functions in daily life activities and social activities whether at home, school or society in general (10).
Assessment of balance is one of the main variables for occupational therapists in evaluating school-age children. Occupational therapists should estimate the child's capability for safe and independent functioning in different environments such as home, school, and society (11). Along these lines, they should assess functional balance in order to address whether a spastic child has the required security and independence to fulfill his/her needs in daily tasks (12).
The test-retest reliability test of the Berg was investigated in children with normal development aged 4 to 13. Reliability was not researched correctly because the needed time period was long for children to complete the static balance items in order to maintain the static posture (11). As a result, due to Berg's burdensome application for children, pediatric balance scale (PBS) was developed as a modified version of Berg (13). The scale of PBS does not require special equipment, performed easily and quickly. This scale is for measuring functional balance of school-age children with mild to moderate motor impairment (12). PBS consists of 14 items in 5 levels and is a criterion reference scale, which assesses the activities that a child should perform at home, school and society in a safe and independent way (14). This test has been translated in Iran and its content validity and face validity have been studied. The content validity index was (CVI=0.97) and the content validity ratio was around 0.80 to 1.00. Moreover, the calculated impact score of face validity was within 2.87 to 4.70 (15).
The purpose of the study was to the assess interrater and test-retest reliability of Persian version of PBS in children with spastic cerebral palsy.

Measurers
Fifty children (27 boys and 23 girls) in the age group of 4-10 yr old with mild to moderate motor impairment (levels 1, 2 and 3 in GMFCS) from the rehabilitation centers in the south of Tehran, Iran were enrolled in Mar 2016 (Table 1). All children were diagnosed with spastic conditions by neurologists.
Before participating in the research, children's parents were asked to sign the informed consent.  (Table 1).

Procedure
The test-retest reliability

Inter-rater reliability
For the inter-rater reliability research, the test was After the performing of each item by the child, both examiners had to record the score and neither of them was permitted to request an item twice from the child for the purpose of changing the score.
After execution of the test for each child, five min were spent to record the total score for the child. . (19).

Test-retest reliability
For the purpose of test-retest reliability regarding the total score of the Persian version of PBS, The correlation coefficient ICC has been calculated.
The amount of ICC is 0.99 as the total point for the Persian version of PBS. since ICC is higher than 0.8, PBS reliability exceeds the high (20) ( Table 2).

Inter-rater reliability
The analysis of correlation coefficient for the purpose of inter-rater reliability regarding the total score of the Persian version of the PBS indicated high reliability (ICC = 0.99) ( Table 2).

The calculation of SEM for both test-retest and
inter-rater reliability is indicated in table 2 for the total score of Persian version of PBS. Since the amount of SEM was less than 10% of total mean score, SEM was acceptable (21).

Item of pediatric balance scale (PBS)
The strength of agreement between inter-rater and test-retest analysis in the Persian version of PBS are shown in Table 3